If you decide to purchase a ticket between San Paulo and Rio, note that each city has a domestic airport that is much closer to downtown and handles most of the domestic flights. You don't want a ticket GIG-GRU or vv but rather (assuming you do this directly on the day of arrival) GIG-domestic SP airport and return domestic SP airport to domestic RdJ airport (sorry but I forget the airport codes for the domestic airports). However, watch out in that searching for example on the GOL website or even using resources such as google flights with throw in some additional airports that are very far from these cities although they can have good LCC fares.